For several decades, surgeons have been performing a wide variety of surgical procedures on the heart. The advent of cardiopulmonary bypass (CPB) allowed surgeons to stop the heart while maintaining a flow of oxygenated blood throughout the rest of the body such that lengthy and highly invasive surgical procedures on the heart could be performed. The CPB apparatus and procedure enabled more widespread practice of cardiac surgery by allowing surgeons to temporarily isolate the heart from the circulatory pathway while extensive and complex repair and reconstruction procedures were performed on the muscles, valves, arteries, etc. of the heart while the heart itself remained static. Although CPB provides the surgeon with the ability to perform certain procedures, connecting the patient to the CPB apparatus is time consuming and traumatic to the patient. In establishing CPB by traditional techniques, the chest is opened by cutting through the sternum and spreading the ribs, large bore cannulas are placed in the patient's venous and arterial system, the heart is stopped by infusion of chemicals, the aorta which supplies blood to the body from the heart is clamped shut, thus separating the heart from the rest of the circulatory system, and the patient's blood supply is circulated outside the body through a mechanical pump and a device to oxygenate the blood.
The CPB procedure has several well-known drawbacks and new information regarding the adverse effects of CPB is continually being discovered. For example, CPB runs the risk of causing ischemic/reperfusion injury in the heart and elsewhere in the body where blood flow is reduced or interrupted and restarted. The problem is particularly significant in the brain where peri-operative strokes and related neurological disorders have been observed in patients following CPB which may result from particles which cause interruptions in the blood supply to the brain. Also, the heart may sustain damage from the CPB process or from the CPB apparatus which results in reduced blood pumping capacity and other irregularities. Furthermore, damage to the blood itself results from passing the blood through the CPB pump and from surface interactions between the patient's blood and the synthetic surfaces inside the pump and associated apparatus. Due to the adverse effects of CPB, surgeons attempt to limit the amount of time that the patient is subjected to CPB and prefer to avoid CPB whenever possible.
Recently, to avoid the need for CPB, techniques and apparatus have been developed to enable surgeons to perform certain types of cardiac surgeries on the beating heart. Principal among these is coronary artery bypass graft surgery (CABG) wherein an obstructed coronary artery, which tends to be located at or near the surface of the exterior of the heart, is bypassed with another source artery or a graft to restore blood flow to the muscles of the heart beyond the obstruction. The prime rationale for the development of the beating-heart procedures is to avoid CPB, and surgeons and engineers are constantly searching for techniques and apparatus to expand the repertoire of beating-heart surgical procedures.
For surgical procedures involving structures and chambers internal to the heart, there is another important rationale for using a beating-heart approach. Many of these procedures require maintaining an opening through the epicardial and myocardial tissue to expose and allow access to the internal target area. An unavoidable result is the introduction of air into the chambers which must be removed to minimize the risk of air bubbles which can lead to stroke. The removal of air in these conventional procedures is accomplished after correcting the defect but prior to resuming normal heart-lung function by closing all myocardial incisions with the exception of a small opening or vent hole and massaging the heart to cause any entrapped air to escape through the opening. The opening is then sutured closed. This technique can be traumatic and damaging to the myocardium and the chambers, and especially to the newly treated target area. Moreover, there is no way of guaranteeing that all air is removed from the heart. Conversely, with a beating-heart approach, the introduction of air could be minimized as atmospheric exposure of the internal chambers must be limited to prevent the loss of blood. In addition, the patient's blood pressure would act to minimize the introduction of any air. Therefore, a need exists for instrumentation that would enable a beating-heart approach to surgical repair of internal cardiac structures while minimizing the risk of air entering the patient's circulatory system.
Surgical procedures involving the repair of structures inside the beating heart, such as the cardiac valves which control and regulate blood flow into, out of, and between the four chambers of the heart, the left and right atria and the left and right ventricles, are very difficult to perform. A surgical procedure on a heart valve is particularly difficult to perform on a beating heart because the valves are located inside the heart and continuously open and close to regulate the flow of blood. Moreover, the valves are immediately proximate to the atria and ventricles which continuously contract to cause blood to flow from the venous system, to the lungs to be oxygenated, and then throughout the body. Still further, the valves must control a volume of blood which may be under considerable pressure due to the contraction of the muscles of the heart. As such, it is extremely difficult to provide a bloodless field within which the surgeon has adequate visibility of the surgical area. Moreover, the continual opening and closing of a valve makes it difficult to perform delicate surgical tasks, such as suturing, which require a high degree of accuracy and precision.
Valve surgery on the beating heart is rendered even more problematic due to the substantial absence of special tools to enable surgical operations inside the beating heart. Among the difficulties inherent in beating heart valvular surgery are the need to work in a moving field, the need to prevent the flow of blood from obstructing the surgical field, and in the case of valvular surgery, the need to isolate a portion of the valve being repaired from the blood flow which is continuing in the remainder of the beating heart, and the need to allow the valves to continue to perform substantially their normal functions during the surgery. Thus, there is a substantial need for instrumentation and new surgical techniques for addressing these difficulties.